Flexible expandable roller conveyors which utilize lazy tong support frames or structures have been widely used for many years. Lazy tongs are structures formed of a set of parallel bars, each of which is pivotally connected at its end points and, in some cases, at its midpoint to corresponding bars in a transversely oriented set of parallel bars so that the structure may be extended and retracted with scissor-like action. Such structures for conveyors are disclosed in U.S. Pat. No. 3,276,558 issued Oct. 4, 1966 to Guske, et al. and U.S. Pat. No. 4,266,650 issued May 12, 1981 to Patel, et al., which are incorporated herein by this reference. The conveyors of those patents include lazy tong structures which are spanned and connected by a number of axles or rods, each of which carries several rollers. Such conveyors are sometimes known as "skate wheel" conveyors because their rollers are, or are similar in construction and appearance to, roller skate wheels.
Lazy tong roller conveyors are particularly useful to move packages and other items from one point to other points in a plant or warehouse, and in loading or unloading trucks, airplanes or containers. They be flexed and extended or retracted with minimum effort to accommodate the desired location, vehicle or container.
U.S. Pat. No. 4,852,712 issued Aug. 1, 1989 to Best, which is incorporated by this reference, discloses a flexible, expandable roller conveyor formed of lazy tong structures. The conveyor employs not only roller axles but also braces rigidly connected to corresponding bars in the lazy tong structures to span the lazy tong structures and support the rollers. The conveyor is more durable and resistent to abuse than previous conveyors because the braces help support the rollers and axles and thus minimize axle bending and deformation which normally occurs in conventional roller conveyors.
The nature of the lazy tong structure allows such conveyors to be retracted and stored in a compact fashion in which successive axles and rollers are positioned nested together immediately adjacent to one another. The distance between successive axles and rollers increases as the roller is expanded to its operative position for conveying articles. The expandable and retractable nature of such conveyors has conventionally precluded using a drive belt for moving articles, so that workers are required to propel articles carried by the conveyors.